1. Field of the Invention
The present invention relates to a method and apparatus for a radiation regulating circuit used in electronic flash devices that use a voltage regulating-style switching element for regulating the radiation of a light emitting tube.
2. Description of Related Art
FIG. 3 is a circuit diagram that shows the construction of a conventional radiation regulating circuit for an electronic flash device. In this diagram, when a power supply switch 100 is closed, a power supply voltage increasing circuit 101 commences operation. Radiation energy is recharged in a main condenser 102, which is connected between a power supply line L1 and a ground line L2 of the power supply voltage increasing circuit 101, and which is also charged in the trigger condenser 104. Also, a zener voltage is generated in the zener diode 110 through a resistor 109. The zener voltage is added to a gate of an insulated gate bipolar transistor (referred to hereafter as "IGBT"), and the collector/emitter gap of the IGBT 108 becomes conductive.
When a radiation commencement signal is input to the trigger terminal TG under these conditions, the anode/cathode gap of the thyristor 105 becomes conductive, a closed loop is formed with the trigger condenser 104 and the primary side of the trigger coil 106, and the charge in the trigger condenser is discharged. In this manner, the trigger voltage is added to the light emitting tube 107 and the light emitting tube commences radiation.
Next, when a radiation termination signal is input to terminal STP while the light emitting tube 107 is radiating, the gate of the IGBT 108 is grounded to the ground line L2 through conduction between the collector/emitter gap of the transistor 111. The collector/emitter gap of the IGBT 108 becomes nonconductive, and the radiation of the light emitting tube 107 ceases.
However, a radiation regulating circuit for an electronic flash device constructed in this manner has no voltage impression doubling circuit for approximately doubling the charging voltage of the main condenser 102 on both ends of the light emitting tube 107. Also, the charging of the trigger condenser 104 is carried out through the resistor 103, but because the resistance value of the resistor 103 is controlled by the thyristor 105, a rapid charge cannot be accomplished because a comparatively large resistance on the order of several hundred kilo-ohms is used. Therefore, high speed repetition of radiation of the light emitting tube has not been possible.